What are doctors' limitations in evaluating products?

Ideally all products used in treating and preventing diseases should undergo prospective, randomized, double blind placebo-controlled trials involving a large number of study subjects. But these studies are costly, and not all proposed studies can be funded. Furthermore, disease prevention studies generally take many years to complete. Therefore, doctors often have to make recommendations based on incomplete knowledge and scientific data. When conclusive proof of effectiveness and safety are not available, doctors sometimes rely on less reliable information from observational studies and even anecdotes.

Even expertly designed and carefully conducted clinical trials may not detect all the adverse effects of a drug or product. Some adverse side effects of a new product may not show up until many (often millions) of users have used it for a long time (months to years).

What is an anecdote in medicine?

In medicine, an anecdote is a treatment response observed on a single person or a number of people. The observations are made outside of a formally conducted, double-blind, randomized, placebo-controlled trial.

What are the shortcomings of anecdotes in medicine?

Anecdotal benefits cannot be distinguished form placebo effects. More often than not, anecdotal benefits cannot be confirmed by double-blind randomized placebo-controlled trials. Therefore, doctors generally are hesitant to recommend treatments solely based on anecdotal evidence. Moreover, potentially serious adverse side effects may only be uncovered by a carefully conducted placebo controlled clinical trial.

However, anecdotal reports of benefits, especially if they seem plausible in a scientific sense, may induce medical researchers to conduct clinical trials to determine the effectiveness and safety of a given product or treatment.

What is a placebo?

A placebo is a biologically inert substance that does not have any effect on the disease under investigation Placebos are given to persons participating in double-blind controlled clinical trials. For example, a placebo can be sugar powder or salt placed in capsules that are made to look exactly like the medication being tested, so that neither the person giving the drug, or the person taking the drug know whether a placebo or the test drug is being administered.

What is a placebo effect?

A placebo effect is a beneficial response of a disease and its symptoms to a placebo. The placebo effect can be found in almost every clinical trial. For example, in all the randomized double-blind, placebo-controlled trials involving ulcer medications, a consistent number of placebo-treated patients will experience ulcer healing and symptom improvement. Thus the only way to prove that a test medication is effective is by demonstrating its superiority over a placebo.

What is an observational study?

An observational study is a retrospective analysis comparing the health status of one group of subjects (for example, women who took folic acid supplements) to another group (for example, women who did not take folic acid supplements). Observational studies can only provide circumstantial evidence. Conclusive proof of treatment benefit has to come from prospective, randomized, and placebo-controlled trials.

• Example: Vitamin A is an antioxidant that was believed to be beneficial in preventing cancer and heart diseases. But randomized prospective placebo-controlled trials not only could not demonstrate any benefit of vitamin A, some studies actually found it harmful in some subjects.

How do doctors recommend treatments for disease prevention?

The decision-making process in disease prevention is necessarily imperfect; it is a combination of judgment, experience, and science. It is a balancing act between being cautious (by doing no harm) versus being proactive.

Safety first

Preventing disease is different from treating diseases. In treating diseases, doctors and patients are often willing to accept a finite degree of risk of side effects in order to achieve a cure or improvement in symptoms. In preventing diseases, doctors are extremely risk adverse. Remember, the first priority in doctoring is to "do no harm". Thus when prescribing an agent for prolonged periods of time to prevent a disease that may or may not occur, the doctor would not want that agent to cause adverse side effects in a healthy person.

• Example: NSAIDs (nonsteroidal antiinflammatory drugs, a class of medications used for arthritis and other inflammatory processes in the body) have been known to inhibit the growth of colon polyps. Colon polyps are precursors to colon cancer. Why aren't doctors recommending NSAIDs to prevent colon cancer? Because prolonged NSAIDs use can have unwanted side effects such as ulcers, intestinal bleeding, and aggravation of liver and kidney diseases. Without prospective randomized placebo controlled trials involving a large number of patients, doctors will not recommend NSAIDs for colon polyp and cancer prevention except in very special and limited situations.